Another major contribution to incorrect data is the unreliability of the inde- 

 pendent measuring instruments themselves. Injection thermometers notably cannot 

 be read any better than ± 0.5 °F and yet are expected to correct the Bathythermo- 

 graph to within 0.1°F. More often than not the injection thermometers are stuck, 

 or are off calibration. There is at present no program requiring these injection ther- 

 mometers to be calibrated. A small expenditure to provide a much more accurate in- 

 jection thermometer would increase the reliability of tremendous quantities of 

 Bathythermograph data which are taken at great cost. 



^ Similarly the bucket thermometer which is normally provided in the kit in 

 which the Bathythermograph comes is entirely inadequate in its readability. Here 

 again a better thermometer should be provided, one which has a readability to the 

 accuracy desired of ± 0.1 °F. 



Another source of error is a poorly designed bucket with which surface samples 

 are taken. There are considerable data to show that the temperature can drop sev- 

 eral degrees between the time the sample is taken and the time it is read, due to 

 high evaporation losses. In other cases the temperature can rise from the radiation 

 of the sun causing heating of the bucket. There are buckets which have been de- 

 signed to provide for good insulation and low evaporation losses, so that the tem- 

 perature of the water when read will be the same as the temperature when the water 

 was actually sampled. 



If in any case the water sampled for independent measurement is not the same 

 as the water through which the Bathythermograph was lowered, the independent 

 measurement will bear no accurate relationship to the Bathythermograph itself. 

 This is more completely discussed in Section 8.3.4. 



8.3.2. Variation in Sets 



The correction of the Bathythermograph involves an independent measure- 

 ment of the water by another instrument. It is assumed that these measurements 

 are made simultaneously. The difference between the reading of two instruments 

 taking simultaneous measurements has been termed discrepancy. This discrepancy 

 is a determinate condition with an indeterminate portion represented by the con- 

 tribution of the errors of the two measuring instruments. 



The variance in a discrepancy can be theoretically caused by three different 

 conditions. (1) The Bathythermograph can contribute 100 7c of the variation due 

 to its variation in set. (2) The independent measuring instrument can contribute 

 100% of the variation, due either to its inaccuracy or to the fact that it is not really 

 measuring a simultaneous condition. (3) The variation and discrepancy can be 

 caused by the combined contribution of both instruments, as pointed out in (1) 

 and (2). 



Where condition (1) is in evidence, then the application of an average discrep- 

 ancy as described in Section 8.1 above does not allow for the variation in set of the 

 Bathythermograph, therefore, it does not correct the Bathythermograph to the ex- 

 tent to which it could be corrected if each individual discrepancy were applied to 

 each Bathythermograph. 



If condition (2) exists, then the varations in the secondary measuring instru- 

 ment can be smoothed out by employing average discrepancies such as described in 

 section 8.1. Where the secondary measurements are considered to be less accurate 

 than the Bathythermograph itself, consideration can even be given to applying no 

 correcting factor at all. Where condition (3) exists, it must be determined whether 

 these conditions lie closer to condition (1) or condition (2) and thence where the 

 individual or average correction should be applied. 



23 



